As a mobile wireless communication method, MIMO (Multiple-Input Multiple-Output) method is known that uses multiple antennae for transmitting radio signals. Especially, MIMO demodulation becomes simplified if MIMO-multiplexed transmission is used for OFDM (Orthogonal Frequency-Division Multiplexing) access. This is because signal separation can be implemented with high precision without being influenced by multipath interference.
LTE (Long Term Evolution) is one of the concrete wireless communication methods that use MIMO-multiplexed transmission for OFDM access.
Various technologies have been proposed for signal separation in MIMO technology.
Among the signal separation technologies in MIMO technology, it is considered to be realistic to adopt the MLD (Maximum-Likelihood Detection) method. This is because interference from adjacent symbols is small in subcarriers of OFDM.
In contrast with OFDM, in a wireless communication method that is greatly influenced by multipath interference such as CDMA (Code Division Multiple Access), a number of adjacent symbols should be taken into account. It is not realistic to use MLD because consideration for a number of symbols induces an exponential increase of processing amount of MLD.
To reduce such a processing amount of MLD, a method is known in that multipath interference is removed by a multipath interference canceler based on MMSE (Minimum Mean Square Error) before processing with MLD.